Hudraulic hammer with control means regulating the volume in an accumulator

ABSTRACT

A hydraulic hammer for treatment of workable solid materials comprising a hammer housing ( 1 ) containing a striking plunger ( 2 ) movable to and fro in a guide to encounter a tool carried by the hydraulic hammer, a hydraulic cylinder unit ( 3 ) comprising a cylinder chamber and a piston ( 14 ) movable therein and connected to the striking body ( 2 ), a hydraulic accumulator ( 19, 20 ), a hydraulic channel between the hydraulic chamber ( 19 ) of the hydraulic accumulator and the cylinder chamber of the hydraulic cylinder unit, and a valve means ( 4, 11, 12 ) for controlling the flow of hydraulic fluid from the hydraulic accumulator to the cylinder chamber of the hydraulic cylinder unit ( 3 ). The valve means comprises a valve ( 4 ), normally closed, in the hydraulic channel, and a valve-opening mechanism ( 11 ) pertaining to the valve ( 4 ), said valve-opening mechanism being actuated by a trigger ( 52 ), and a control means ( 42, 44, 54 ) are provided to prevent activation of the valve-opening mechanism ( 11 ) before the hydraulic chamber of the hydraulic accumulator has been filled with a volume of hydraulic fluid selectable in advance.

The invention relates to a hydraulic hammer of the type revealed in the preamble to claim 1.

It is known that striking hydraulic hammers are effective for disintegrating a large quantity of material in a short space of time, e.g. for making holes or carrying out wrecking in concrete and for drilling holes for ore-mining.

SE-B414001 describes a hydraulic hammer of this type. Such a hydraulic hammer comprises a hammer housing with a hydraulic unit. The hammer housing comprises a hydraulic cylinder unit with a piston which acts on a striking head controlled in a guide and is shown to impart impact energy to a tool.

The hammer housing contains a hydraulic accumulator comprising a hydraulic chamber and a gas chamber, separated by a movable membrane or a movable plunger. Hydraulic fluid is supplied by a hydraulic pump to the hydraulic hammer of the hydraulic accumulator. A hydraulic channel connects the accumulator and the hydraulic cylinder unit. A valve means is provided for controlling the flow of hydraulic fluid to and from the hydraulic cylinder unit.

In the known hydraulic hammer the valve means is structurally pre-set so that the piston of the hydraulic cylinder unit, and thus the tool, acquire a continuous to and fro movement as long as the hydraulic fluid is supplied by the hydraulic pump. It is not possible to regulate the valve means so that only one stroke is performed, nor is it possible to choose the striking power for individual strokes.

In tasks where it is desired to chisel a certain shape from a block of stone or some other mineral, or to divide the block into specific slabs or pieces, access is desirable to a hydraulic hammer with which individual strokes of the tool can be triggered and also, if so desired, a continued series of hammer strokes can be performed.

A hydraulic hammer with which the stroke frequency of the tool can be varied and/or with which the power of individual hammer strokes can be regulated is naturally also desirable. Such properties are desirable, for instance, if a hydraulic hammer is to be used for chiselling the outer contours of a gravestone, for instance, when slabs of slate shall be obtained from blocks of slate, and when slabs of various thickness shall be chiselled from a stone block by establishing a fracture indication which, upon continued working, produces a natural area of fracture in the stone block and releases a slab at an end surface of the block.

One purpose of the invention is therefore to provide a hydraulic hammer of the type mentioned in the introduction, that will permit individual working strokes to be triggered. Another purpose is to provide a hydraulic hammer that easily enables optional adjustment of striking power and/or the performance of a continuous series of tool strokes, and/or permits simple setting of the stroke frequency of the tool during continuous striking.

Yet another purpose of the invention is to provide a hydraulic hammer the striking head of which, driven by the piston of the hydraulic cylinder unit, can be controlled with generous radial clearance in a guide provided therefor.

The purpose is achieved fully or partially by means of the invention.

The invention is defined in the appended claim 1.

Embodiments of the invention are described in the appended subordinate claims.

An important feature of the invention is that the valve means comprises a valve, normally closed, in the hydraulic channel, and that a manually operated trigger is arranged to permit activation of a valve-opening device provided a predetermined oil pressure has been established in the accumulator. The pressure in the accumulator can be established by pumping in a volume of hydraulic fluid, selectable in advance, into the accumulator from a pressure source for hydraulic fluid, e.g. a hydraulic pump. The hydraulic pump may be of a type that supplies a volume that is proportional to the total angle of rotation of the pump during an operating cycle. It is then simple to control the pump so that it rotates a chosen total angle of rotation during an operating cycle, that corresponds to a predetermined supply of hydraulic fluid to the hydraulic accumulator. The accumulator generally contains a gas spring. The gas spring can be adjusted by establishing a larger or smaller amount of gas in the gas chamber of the accumulator.

In preferred embodiments the control means of the hammer is designed to permit performance of a single working stroke when the trigger is actuated. Alternatively the control means can be re-set so that when a trigger is actuated a series of strokes will be performed, subsequent strokes not being triggered until the hydraulic chamber has been provided with the pre-selected volume of pressure oil.

In a particularly preferred embodiment of the invention, on the side turned away from the hydraulic fluid, the piston of the hydraulic cylinder unit is provided with a rod, the cross-sectional dimensions of which are considerably less than the inner diameter of the chamber of the hydraulic cylinder unit and its outlet opening for the rod, so that the forward end of the rod is swivel-connected to a strking head that is controlled in a guide with relatively large radial clearance. The swivel-connection can be formed by the forward end of the rod being rounded, preferably spherically, and being received in a corresponding recess arranged centrally in the striking head. Considerable radial clearance for the striking head in its guide is necessary for practical operation of the hydraulic hammer. The piston of the hydraulic cylinder unit is permitted a certain inclination but since the peripheral seal between the piston and the wall of the hydraulic cylinder unit usually consists of an elastomeric sealing element, such inclination is permissible and incurs little risk of leakage.

The invention will be described by way of example in the following with reference to the accompanying drawings.

FIG. 1 shows schematically a section through a hydraulic hammer in accordance with the invention.

FIG. 2 shows a sectioned view taken along the line A-A in FIG. 1.

FIG. 3 shows a detailed enlargement of a valve in the hydraulic pipe between the hydraulic cylinder unit and the hydraulic accumulator.

FIG. 4 illustrates schematically the hydraulic hammer in accordance with the invention, with its control means.

The hydraulic hammer shown in FIGS. 1-3 has a connection 18 for hydraulic fluid from a hydraulic pump. The hammer has a hammer housing 1 containing a hydraulic accumulator comprising a cylinder with a plunger 6 sealing against the cylinder walls and displaceable along the cylinder, dividing this into a gas chamber 20 and a hydraulic fluid chamber 19 which communicates with the connection gate 18. The gas chamber 20 is closed but the wall of the gas chamber has a through-pipe with a valve 10 permitting gas to be supplied to the gas chamber 20. The plunger 6 is provided with a non-return valve for refilling of the oil chamber 19. A throttle ring 8 is also provided and serves to retard the displacement speed of the plunger 6. The hydraulic hammer also comprises a hydraulic cylinder unit 3 including a cylinder chamber and a piston 14 driving a striking head 2 which is journalled with relatively large radial clearance in a guide for the purpose. At the forward end of the hydraulic hammer is a chuck 16 with a clip 17 for retaining a tool in the form of a chisel. The striking head 2 encounters the rear end 15 of the tool. A first spring 13 is provided to return the striking head and thus the piston of the hydraulic cylinder unit in order to return hydraulic fluid from the hydraulic cylinder unit in conventional manner. Between the hydraulic accumulator and the chamber of the hydraulic cylinder unit is a channel 180 that carries hydraulic fluid and contains a valve 4 which is normally closed. A spring 12 is shown arranged to pre-stress the plunger 5 of the valve 4 to closed state. An electromagnet 11 is arranged, when provided with electricity, to force the valve 4 to open state, against the action of the spring 12. The electromagnet 11 is provided with current by activation of a trigger 52 that may be placed on the hydraulic hammer or somewhere else. The trigger 52 is shown in the form of a switch in a current-supply wire to the electromagnetic 11.

It should be clear that instead of the electromagnet 11 and a trigger 52 of current switching type, a valve opener actuated by hydraulic fluid can equally well be used to operate the valve 4. From an electrically controlled hydraulic valve a pressurized flow of hydraulic fluid is released through a pipe to the valve opener, its piston then opening the valve 4.

A hydraulic pump 40 is arranged to charge the accumulator 19 to a pre-selected pressure. When this pressure has been reached the valve 4 can be opened so that the piston 14 is displaced and executes a stroke of the hammer. Thereafter the spring 13 returns the striking body 2 and thus the piston 14, and the gas spring 20 returns the accumulator piston so that hydraulic fluid is forced out of the hammer via the pipe 55, a charging valve 56 arranged in the pipe 55 and set in open position, and a relief valve 58 as set in open position, to the tank.

The electromagnet 11 is controlled by a control unit 42, shown connected to a switch 55 which in one position ensures that only one stroke of the hammer can be triggered by actuation of the trigger 52, so that the trigger 52 must first be unloaded before a new stroke of the hammer can be triggered with the trigger 52, providing the pump 40 has had time to place the accumulator 19, 20 under a pre-selected pressure. This pressure is normally established by the pump 40 being caused to pump a pre-selected volume of hydraulic fluid into the accumulator 19, 20.

The switch 55 has a second position that controls the control unit 42 to permit the hammer to perform a series of strokes as long as the trigger 52 is kept actuated, after which once again a stroke can be triggered only after the accumulator 19, 20 has been charged to a predetermined state as regards pressure or filling volume.

The control unit 42 may be a conventional type of PLC control unit. The accumulator 19, 20 is charged for one stroke of the hammer as follows:

The control program of the control unit 42 permits an electric voltage to be applied to the electromagnet of the relief valve 58 and to the electromagnet 11 of the valve 4, so that hydraulic fluid in the hammer can be emptied through the filling valve 56 and pipe 55. The filling valve is normally open in uninfluenced state, so that the spring 13 can press back the striking head 2 and piston 14. The hydraulic fluid is then conveyed to the tank.

Thereafter the unit 42 cuts the voltage over the electromagnets of the valves 4 and 58 so that they close. The pump 40 which rotates at a constant rate of revolution, and thus pumps hydraulic fluid to the tank, is now forced to start supplying its hydraulic outflow to the accumulator chamber 19. At the same moment the control unit 42, using an internal counter, is arranged to start counting pulses from a pulse transducer 44 connected to the pump motor. Each pulse corresponds to a predetermined small angle of rotation for the pump and an equivalent volume of hydraulic fluid, which is fed out by the pump 40. A predetermined number of pulses can be set on the control unit 42, using the setting device 54. The setting device 54 may be of potentiometer type. When the control unit 42 has counted a number of pulses from the pulse transducer 44 corresponding to the number set with the setting device 54, the filling valve 56 is closed and the relief valve 58 opened so that the pump 40 can continue working without load and substantially without energy losses. By setting a higher or lower number of pulses with the setting device 54 the hydraulic accumulator 19, 20 can be filled with a correspondingly larger or smaller amount of hydraulic oil so that the accumulator acquires a volume of pressure oil to give the desired striking power.

Upon activation of the trigger 52 the control unit 42 is influenced to apply a voltage over the electromagnet 11 so that the valve 4 opens.

The control unit 42 is arranged to drive the motor M at an optional speed. The speed can be changed by a corresponding adjustment of the setting device 48. Changing the speed of the motor also changes the time required for each striking cycle, from charging to emptying of the hammer. The switch 50 in the current-supply line to the units 52, 54, 55, 48 may suitably contain a switch 50 for disconnecting the current to the hydraulic unit. 

1. A hydraulic hammer for treatment of workable solid materials comprising a hammer housing (1) containing a striking plunger (2) movable to and fro in a guide to encounter a tool carried by the hydraulic hammer, a hydraulic cylinder unit (3) comprising a cylinder chamber and a piston (14) movable therein and connected to the striking body (2), a hydraulic accumulator (19, 20), a hydraulic channel between the hydraulic chamber (19) of the hydraulic accumulator and the cylinder chamber of the hydraulic cylinder unit, and a valve means (4, 11, 12) for controlling the flow of hydraulic fluid from the hydraulic accumulator to the cylinder chamber of the hydraulic cylinder unit (3), characterised in that the valve means comprises a valve (4), normally closed, in the hydraulic channel, and a valve-opening mechanism (11) pertaining to the valve (4), said valve-opening mechanism being actuated by a trigger (52), and in that control means (42, 44, 54) are provided to prevent activation of the valve-opening mechanism (11) before the hydraulic chamber of the hydraulic accumulator has been filled with a volume of hydraulic fluid selectable in advance.
 2. A hydraulic hammer as claimed in claim 1, characterised in that the control means comprises means for sensing the volume of hydraulic fluid supplied by the pump to the hydraulic accumulator, and means (54) for pre-setting a selectable quantity of hydraulic fluid that can be supplied to the hydraulic accumulator.
 3. A hydraulic hammer as claimed in claim 2, characterised in that a hydraulic pipe (55) between the pump (40) and the hydraulic hammer contains a valve (56) which is set in closed position by control means (42) when the pre-selected volume of hydraulic fluid has been supplied to the hydraulic accumulator and, after having triggered striking of the hydraulic hammer, is returned to open position by the control unit (42).
 4. A hydraulic hammer as claimed in claim 3, characterised in that the pump (40) is arranged to supply a volume of hydraulic fluid that is proportional to the total angle of rotation of the pump (40) during an operating cycle, in that a pulse transducer (44) is arranged to sense the total angle of rotation of the pump, and in that the control means is arranged to disconnect the flow of pressure oil to the hydraulic accumulator when the pump has rotated a predetermined total angle of rotation, the size of which is adjustable by a setting device (54) connected to the control means (42).
 5. A hydraulic hammer as claimed in claim 1, characterised in that on the side turned away from the hydraulic fluid the piston (14) of the hydraulic cylinder unit (3) is provided with a rod (141), the cross-sectional dimensions of which are considerably less than the inner diameter of the chamber of the hydraulic cylinder unit and its outlet opening for the rod (141), so that the rod can be angled in relation to the shaft of the hydraulic cylinder unit, and in that the end of the rod turned away from the piston is swivel-connected to the striking body (2), and in that the striking body (2) is controlled with radial clearance in a guide.
 6. A hydraulic hammer as claimed in claim 5, characterised in that the swivel connection between the forward end of the rod and the striking body comprises a spherical swivel joint.
 7. A hydraulic hammer as claimed in claim 6, characterised in that the swivel joint comprises a spherically rounded forward end of the rod and a corresponding recess in the adjacent end of the striking body (2).
 8. A hydraulic hammer as claimed in claim 5, characterised in that the rod (141) is rigidly connected to the piston (14).
 9. A hydraulic hammer as claimed in claim 2, characterised in that on the side turned away from the hydraulic fluid the piston (14) of the hydraulic cylinder unit (3) is provided with a rod (141), the cross-sectional dimensions of which are considerably less than the inner diameter of the chamber of the hydraulic cylinder unit and its outlet opening for the rod (141), so that the rod can be angled in relation to the shaft of the hydraulic cylinder unit, and in that the end of the rod turned away from the piston is swivel-connected to the striking body (2), and in that the striking body (2) is controlled with radial clearance in a guide.
 10. A hydraulic hammer as claimed in claim 3, characterised in that on the side turned away from the hydraulic fluid the piston (14) of the hydraulic cylinder unit (3) is provided with a rod (141), the cross-sectional dimensions of which are considerably less than the inner diameter of the chamber of the hydraulic cylinder unit and its outlet opening for the rod (141), so that the rod can be angled in relation to the shaft of the hydraulic cylinder unit, and in that the end of the rod turned away from the piston is swivel-connected to the striking body (2), and in that the striking body (2) is controlled with radial clearance in a guide.
 11. A hydraulic hammer as claimed in claim 4, characterised in that on the side turned away from the hydraulic fluid the piston (14) of the hydraulic cylinder unit (3) is provided with a rod (141), the cross-sectional dimensions of which are considerably less than the inner diameter of the chamber of the hydraulic cylinder unit and its outlet opening for the rod (141), so that the rod can be angled in relation to the shaft of the hydraulic cylinder unit, and in that the end of the rod turned away from the piston is swivel-connected to the striking body (2), and in that the striking body (2) is controlled with radial clearance in a guide. 